Fears are growing that dangerous toxins may be seeping from a Czech chemical plant and washing north through Germany in the waters of the swollen River Elbe.

German Environment Minister Juergen Trittin is to visit the Spolana plant, 15 kilometres north of Prague, on Tuesday to seek information on the alleged leak of dioxins and mercury from facilities still under water.

Czech police have begun an investigation into the plant, amid allegations that chemicals may not have been stored correctly.

There is already widespread concern about the spread of disease by animal carcasses swept along in the waters, which have left large swathes of the Czech Republic and central and eastern Germany under water.

Towns in northern Germany are now on alert as the swollen Elbe surges towards Hamburg, where it empties into the North Sea.

The number of people killed in Germany has now reached 18 while across Europe more than 100 have perished in the floods.

Contamination concerns

The Czech authorities say there is no risk of an environmental catastrophe at the Spolana plant but admit that the situation is serious and there is an ongoing threat of toxic leaks.

Chlorine leaked from Spolana on Thursday

A cloud of deadly chlorine gas was released when the plant was swamped by the floods last week but it is believed to have been too small to have posed a threat.

"It is clear that dangerous materials were there and it appears that they were not properly secured and there were problems with how they were registered," a Czech police spokesman, Miroslav Antl, told Pravo newspaper.

On Sunday, specialists began pumping chlorine from the plant's stores into separate tanks.

Mr Trittin expressed grave concerns about contamination from the plant when it was submerged last week, and his visit, accompanied by Czech Environment Minister Libor Ambrozek, is aimed at easing German concerns.

Disease fears

At home, Mr Trittin on Tuesday morning played down fears sparked by German media reports that the flooding could cause serious outbreaks of disease, including hepatitis and dysentery.

He said that "normal rules of hygiene", including washing hands should be followed when returning to properties that had been flooded and that animal carcasses should be disposed of as quickly as possible.

People are asked to take hygiene precautions when returning home

Authorities in the Czech Republic, have also warned that debris left by the floods is a health risk.

Many sewage treatment plants in Prague were forced to halt operations and fears of disease and structural damage to buildings have kept many residents from returning to their homes.

However, the roads into Prague were reported to be choked on Tuesday as evacuees returned home.

Northern towns on alert

Towns and villages along the northern stretch of the Elbe remain on a state of alert with thousands of people evacuated.

But the city of Magdeburg escaped the worst when waters peaked there overnight but did not breach the sandbag defences erected by volunteers.

In the state of Lower Saxony, initial evacuations in several towns are under way. In the town of Luechow-Dannenberg water levels rose by 60 centimetres (23.6 inches) in 24 hours.

Four million Germans have already been affected, forcing well over 100,000 to flee their homes.

The German Government decided on Monday to delay for a year planned tax cuts to finance the cost of clean-up operations.

Spokesman Joerg Mueller said the decision would allow about 7.5 billion euros ($7.3bn) to be released.

Private donations have also amassed tens of millions of euros in funds for the affected areas.

European Commission President Romano Prodi has promised EU aid for the four countries - Austria, Germany, the Czech Republic and Slovakia - worst affected by the disaster.